1. Field of the Invention
This invention relates to the characterization and processing of optical beams, and more particularly to a system and method for converting the spatial intensity spectrum of a light beam to a positional mapping, or for deflecting light to achieve optical intensity-to-position mapping or to implement a switching mechanism.
2. Description of the Related Art
The distribution of optical intensities across a single light beam or a series of separate light beams may form the basis for optical computing and logic processing by first converting the distribution of light intensities to a positional mapping, and then operating upon the signal at each different position to perform the desired computing or processing. The cross-section of a light beam 2 can be envisioned as an aggregation of a large number of pixel locations 4, as illustrated in FIG. 1. Because the pattern of light intensity at each different pixel location can be imaged or mapped elsewhere in the system, this pattern may be employed as an information coding system. For various computing and logic processing purposes it is desirable to group the various pixels by their respective optical intensity levels, rather than by their spatial positions within the beam. In other words, it is desirable to be able to convert the spatial intensity pattern of beam 2 to a positional mapping 6, in which all pixels having a common optical intensity are mapped to a common position on a distance spectrum. In the example of FIG. 1 it is assumed, for a simple special case, that the optical intensity levels are grouped into a limited number of discrete levels, rather than extending over a continuum of intensities. Thus, the mapping process may yield a number of discrete spikes 8 which are separated by positional distance, the height of each spike varying with the number of pixels having an optical intensity corresponding to the position of the spike. This representation is called a histogram. Where separate input light beams are presented, such as in discrete optical fibers, it may likewise be desirable to switch the separate beams among various output locations in accordance with their intensities.
A system which accomplishes the desired intensity-to-position mapping is described in U.S. Pat. No. 4,351,589 to Pierre H. Chavel et al., assigned to Hughes Aircraft Company, the assignee of the present invention. The patent discloses the use of liquid crystals to produce variable gratings, which diffract incoming light by varying amounts depending upon the grating period. The optical intensities at the different locations in an input light beam control the grating period at corresponding locations in the liquid crystal media. The variable gratings were employed to convert the spatial intensity distribution within the input beam to a positional mapping of intensities, from which the desired computing and logic functions could be accomplished. Applications of this variable grating mode (VGM) device are disclosed in an article by B. H. Soffer et al., "Optical Computing With Variable Grating Mode Liquid Crystal Devices", 1980 International Optical Computing Conference, SPIE Vol. 232, pages 128-136.
While it facilitates optical data and image processing and optical logic and computing, the variable grating device disclosed in the patent in its present state of development has somewhat slow response times, and works only at low temporal frequencies.
A paper has been published disclosing a single prismatic wedge of liquid crystal, across which a variable voltage is applied to deflect a light beam, M. A. Muriel and J. A. Martin-Pereda, "Digital Light Beam Deflector with Liquid Crystals", 1980 European Conference on Optical Systems and Applications (Utrecht), SPIE Vol. 236, pages 386-388. The amount of deflection which a light ray undergoes after crossing the wedge is said to depend upon the applied voltage. However, the light was subject to a large amount of scattering in transit through the wedge, and the single cell disclosed was not suitable for use in intensity-to-positional mapping. The response time is also slow.
A related technological issue involved an attempt to control the focal length of a lens by means by an applied voltage. This was described in an article by Susumu Sato, "Liquid-Crystal Lens-Cells with Variable Focal Length", Japanese Journal of Applied Physics, Vol. 18, No. 9, September 1979, pages 1679-1684. In this approach liquid crystal cells shaped like a plano-convex lens or a plano-concave lens were prepared. Electric or magnetic fields were applied across the lens-cell to vary its focal length. The authors encountered excessive light scattering and slow response time due to the thickness of the liquid crystal cell.